Method of transmitting feedback information in a multi-input, multi-output (MIMO) system

ABSTRACT

A method of transmitting feedback information in a Multi-Input, Multi-Output (MIMO) system is disclosed. In the method, a mobile station (MS) which determines to transmit feedback information and feedback type to a base station (BS) without solicitation from the BS, wherein the feedback type is transmission antenna type, and transmits the feedback information using a MIMO mode feedback extended subheader, wherein the MIMO mode feedback extended subheader appears between a Medium Access Channel (MAC) header and a payload.

This application is a continuation of U.S. application Ser. No.11/367,917, filed Mar. 3, 2006, now U.S. Pat. No. 7,633,906, whichpursuant to 35 U.S.C. §119(a) claims the benefit of Korean ApplicationNo. P10-2005-17999, filed on Mar. 4, 2005, which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of transmitting feedbackinformation, and more particularly, to a method of transmitting feedbackinformation in a Multi-Input, Multi-Output (MIMO) system.

2. Discussion of the Related Art

A Multi-Input, Multi-Output (MIMO) system seeks to improve frequencyefficiency and capacity of a network link by using a plurality ofantennas in a base station (BS) as well as in a mobile station (MS). Assuch, the MIMO system has been receiving much attention as usefultechnology for transmitting high speed data in a mobile wirelesscommunication system.

In a closed-loop MIMO system having plurality of antennas, the MSreceives data transmitted from the BS and estimates channel informationof each channel. Then the MS uses the estimated channel information toobtain a weight value which is subsequently transmitted as feedbackinformation to the BS. After receiving the feedback information, the BSapplies the weight value to input data so as to more effectively andefficiently transmit the input data to the MS.

In an Orthogonal Frequency Division Multiple/Orthogonal FrequencyDivision Multiple Access (OFDM/OFDMA) system, the BS receives from theMS various types of feedback information to be applied to downlinksignals. In the MIMO system, there are various modes that can be appliedfor transmission based on the data transmission scheme used by themultiple antennas of the transmitting end. These modes include a SpaceTime Transmit Diversity (STTD), a Spatial Multiplexing (SM), and aclosed-loop SM. Furthermore, in the closed-loop MIMO system, there arefive (5) types of feedback information that can be transmitted to the BSfrom the MS.

The first type is an antenna grouping index. The antenna grouping indexapplies when the closed-loop STTD scheme is used. More specifically, apair of antennas, which has achieved STTD, can be changed based onchannel status, and an index of the optimum pair of antennas areprovided by the MS to the BS.

The second type is an antenna selection index. The antenna selectionindex applies when a closed-loop STTD scheme or a SM scheme is used.More specifically, a specified number of antennas having best channelstatus are selected from a plurality of antennas, and indices of theselected antennas are sent to the BS.

The third type is a precoding codebook index. The precoding codebookindex applies when a closed-loop SM scheme is used. More specifically,the precoding matrix codebook, which is multiplied to the transmissionsignal at the BS transmission antenna group, are retained by both the BSand the MS, and the MS selects and provides ith the optimum precedingmatrix with respect to channel status to the BS.

The fourth type is a directed precoding matrix value. The directedprecoding matrix value applies when a closed-loop SM scheme is used.More specifically, the MS directly provides a value of the precodingmatrix. The precoding matrix is multiplied to the transmission signal atthe BS transmission antenna group.

The fifth type is a number of streams. The number of streams applieswhen a STTD scheme or a SM scheme is used. More specifically, the MSprovides a number of transmission signals, which can be used to achieveoptimum transmission capacity in either scheme, to the BS. Here, thenumber of transmission signals is identical to the number ofsimultaneously transmitted transmission symbols.

In addition to five (5) types of feedback information, the feedbackinformation can include the MS selected MIMO mode a permutation schemeassociated with the selected mode. The details of which are providedbelow.

In the OFDM/OFDMA wireless communication system, the MS determines thepermutation scheme and transmits the determined permutation scheme tothe BS in a form of feedback information. Here, determining permutationscheme means that the MS determines the scheme by which data in afrequency broadband for data transmission is allocated and arranged.That is, the MS selects any one of a Full Usage Sub-Carrier (FUSC), aPartial Usage Sub-Carrier (PUSC), and an Adjacent Sub-CarrierPermutation schemes.

Transmitting the feedback information of the MIMO mode and thepermutation scheme selected by the MS or the weight to be applied fordownlink transmission in the closed-loop MIMO system can be accomplishedusing the following processes. First, the BS transmits to the MSinformation containing the feedback types to be used in sending feedbackinformation to the BS and the feedback time period according which theMS should transmit feedback information to the BS. This information canbe transmitted using any one of an Information Element (IE) forproviding a Channel Quality Information Channel (CQICH), a fast feedbackallocation subheader which is transmitted together with data, and aFeedback Polling IE which is used by the BS to allocate uplink resource.

After receiving the information the feedback types and the feedbackperiod, the MS can use a fast feedback channel on an allocated frame tosend feedback information periodically or use a feedback header in theallocated uplink resource to transmit feedback information periodicallyor non-periodically. If there is data to be transmitted to the BS, theMS uses the subheader to transmit the data.

The following problems exist with respect to the above description.First, a procedure for transmitting (reporting) a MIMO mode andpermutation scheme selected by the MS is different from a procedure fortransmitting (reporting) determined weight. Second, although there arecurrently three (3) types of methods for transmitting weights to beapplied to downlink transmission, there is no information as to whichmethod should be applied. Lastly, there is no disclosure relating to amethod of transmitting a direct precoding matrix value.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method oftransmitting feedback information in a Multi-Input, Multi-Output (MIMO)system that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a method oftransmitting feedback information in a Multi-Input, Multi-Output (MIMO)system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of transmitting feedback information in a Multi-Input,Multi-Output (MIMO) system includes a mobile station (MS) whichdetermines to transmit feedback information and feedback type to a basestation (BS) without solicitation from the BS, wherein the feedback typeis transmission antenna type, and transmits the feedback informationusing a MIMO mode feedback extended subheader, wherein the MIMO modefeedback extended subheader appears between a Medium Access Channel(MAC) header and a payload.

In another aspect of the present invention, the MS generates a ProtocolData Unit (PDU) which includes a Medium Access Channel (MAC) header, anextended subheader group and a payload, wherein the MAC header includesinformation on whether or not an extended subheader group appears afterthe MAC header, and wherein the extended subheader group includes a MIMOmode feedback extended subheader. Furthermore, the MS transmits the PDUwhich includes the MAC header and the MIMO mode feedback extendedsubheader, wherein the MIMO mode feedback extended subheader includes arequest for a change in an antenna transmission type.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 illustrates an example of data structure of a Medium AccessControl (MAC) Protocol Data Unit (PDU) in an OFDMA broadband wirelessaccess system;

FIG. 2 illustrates a detailed description of the ESF of FIG. 1;

FIG. 3 illustrates an example of a process between a mobile station (MS)and a base station (BS) according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In the conventional art, there is no method of notifying existence of afast uplink feedback subheader. Table 1 and Table 2 illustrate examplesof data format of a mode selection feedback subheader.

TABLE 1 Length Name (bits) Description Feedback Type 4 Indicate the typeof feedback (See Table 2) Feedback Content 4 Content of the feedback

TABLE 2 Feedback Type Description 0b0000 MIMO mode and permutation. Ifset to this type, the feedback content is described in Table 30b0001-0b1111 Reserved

The mode selection feedback subheader is used by the MS after a MIMOmode and a permutation scheme to be used for transmission is selected.The mode selected feedback subheader is not used by itself. That is, asillustrated in FIGS. 1 and 2, an Extended Subheader Field (ESF) notifiesthe existence and contents of the mode selected feedback subheader. Morespecifically, FIG. 1 illustrates an example of data structure of aMedium Access Control (MAC) Protocol Data Unit (PDU) in an OFDMAbroadband wireless access system. FIG. 2 illustrates a detaileddescription of the ESF of FIG. 1.

As illustrated in FIG. 1, by including an indication field to indicatewhether an ESF exists or not, more and/or different types of subheaderscan be included between the header and the subheader. To putdifferently, since the ESF field is comprised of 2 bytes, a bitmap of 11bits can be used to indicate existence of 11 subheaders and remaining 5bits can be used to indicate size(s) of subheader(s).

Table 3 shows a MIMO mode and permutation scheme mapped to a 4-bitpayload.

TABLE 3 Value Description 0b0000 STTD and PUSC/FUSC permutation 0b0001STTD and adjacent-subcarrier permutation 0b0010 SM and PUSC/FUSCpermutation 0b0011 SM and adjacent-subcarrier permutation 0b0100Closed-loop SM and PUSC/FUSC permutation 0b0101 Closed-loop SM andadjacent-subcarrier permutation 0b0110 Closed-loop SM + Beamforming andadjacent- subcarrier permutation 0b1000~0b1111 Reserved

Table 4 is an example of a data type of a fast uplink feedback subheaderwhich is transmitted as feedback to the BS after the MS determinesweight for downlink transmission quality enhancement in a closed-loopMIMO system.

TABLE 4 Length Name (bits) Description Feedback type 2 Indicate the typeof feedback. The same mapping applies as the Feedback type field intable 5. Feedback content 6 Content of the feedback. The same mappingapplies as in table 5.

Table 5 describes an example of feedback contents. In Table 5, the indexvalue, which indicates antenna grouping, antenna selection, andprecoding codebook, can use any three values from 0b101110˜0b110110.

TABLE 5 Value Description 0b101000 STTD and PUSC/FUSC permutation0b101001 STTD and adjacent-subcarrier permutation 0b101010 SM andPUSC/FUSC permutation 0b101011 SM and adjacent-subcarrier permutation0b101100 Hybrid and PUSC/FUSC permutation 0b101101 Hybrid andadjacent-subcarrier permutation 0b101110~0b110110 Interpretationaccording to table 296e, 296f or 296g, depending on in antenna grouping,antenna selection or a reduced preceding matrix code book is used.0b110111 Closed loop preceding with 1 stream. 0b111000 Closed looppreceding with 2 stream 0b111001 Closed loop preceding with 3 stream.0b111010 Closed loop preceding with 4 stream. 0b11101~0b111111 reserved

To improve downlink channel capability, the BS transmits feedback typeand feedback period to the MS so as to receive channel estimation valueand a method of transmitting the most appropriate MIMO mode and weightvalue in the closed-loop MIMO system. It is also possible to transmitMIMO mode change request or use a method for transmitting precodingweight/antenna weight as feedback information to the BS withoutsolicitation from the BS.

If the BS requests for or solicits a specific feedback type, the MStransmits an indicator for indicating the specific feedback type andcorresponding the feedback content as feedback to the BS. Even if the MSdoes not receive any request or solicitation from the BS, the MS canvoluntarily select and transmit desired/preferred MIMO mode or use amethod for transmitting precoding weight/antenna weight to the BS.

As an example of transmitting a specific feedback type to the BS, if theMS has data to transmit to the BS, preferably, the MS transmits feedbackinformation by including the indicator used to indicate the feedbacktype and the feedback content in the subheader of the MAC PDU (e.g.,MIMO mode feedback subheader).

As described above, FIG. 1 illustrates an example of a MAC PDU datastructure according to an embodiment of the present invention. In FIG.1, the existence of the MIMO mode feedback subheader according to theembodiment of the present invention is indicated via the ESF, whichoccupies a portion of the header. Moreover, the subheader types that canbe employed by the ESF are determined, and at the same time, the size ofthe ESF is determined based on characteristics of the subheaders (e.g.,number of subheaders and types of subheaders).

FIG. 3 illustrates an example of a process between the MS and the BSaccording to an embodiment of the present invention. In FIG. 3, the BStransmits the MAC PDU which includes the ESF and subheader to indicatethe feedback type. Upon receipt, the MS determines the location of thesubheader(s) that can be included between the header and the payload.The MS further determines the necessary information for the feedbacktype. Thereafter, the MS transmits to the BS the header, without thepayload, to notify the BS of the determined feedback type.

Table 6 shows an example of a bitmap structure which notifies theexistence of the MIMO mode feedback subheader within the ESF.

TABLE 6 ESF bit Name Length(bytes) #0 (LSB) UL MIMO mode feedbacksubheader 1 #1 Reserved

Table 7 depicts an example of the contents of a MIMO mode feedbacksubheader. In FIG. 7, ‘Feedback type’ has a length of 2 bits andfunctions as an indicator for the contents for which the MS seeks tomake a request. Furthermore, ‘Feedback content’ has a length of 6 bitsand can have the capability to distinguish the applied methods in0b10110˜0b110110 of Table 5.

TABLE 7 Length Name (bits) Description Feedback 2 00: Mode selection andPermutation and Stream type number 01: Antenna grouping 10: Antennaselection 11: Preceding matrix code book Feedback 6 If Feedback type is‘00,’ refer to Table 5 contents If Feedback type is ‘01’, refer to Table8 If Feedback type is ‘10’, refer to Table 9 If Feedback type is ‘11,’refer to Table 10

TABLE 8 Value Description 0b101110 Antenna Group A1 for rate 1 For3-antenna BS, See 8.4.8.3.4 For 4-antenna BS, See 8,4,8,3,5 0b101111Antenna Group A2 for rate 1 0b110000 Antenna Group A3 for rate 10b110001 Antenna Group B1 for rate 2 For 3-antenna BS, See 8.4.8.3.4 For4-antenna BS, See 8.4.8.3.5 0b110010 Antenna Group B2 for rate 20b110011 Antenna Group B3 for rate 2 0b110100 Antenna Group B4 for rate2 (only for 4-antenna BS) 0b110101 Antenna Group B5 for rate 2 (only for4-antenna BS) 0b110110 Antenna Group B6 for rate 2 (only for 4-antennaBS)

TABLE 9 Value Description 0b101110 Antenna selection option 0 0b101111Antenna selection option 1 0b110000 Antenna selection option 2 0b110001Antenna selection option 3 0b110010 Antenna selection option 4 0b110011Antenna selection option 5 0b110100 Antenna selection option 6 0b110101Antenna selection option 7 0b110110 reserved

TABLE 10 Value Description 0b101110 Reduced Preceding matrix code bookentry 0 0b101111 Reduced Preceding matrix code book entry 1 0b110000Reduced Preceding matrix code book entry 2 0b110001 Reduced Precedingmatrix code book entry 3 0b110010 Reduced Preceding matrix code bookentry 4 0b110011 Reduced Preceding matrix code book entry 5 0b110100Reduced Preceding matrix code book entry 6 0b110101 Reduced Precedingmatrix code book entry 7 0b110110 reserved

In the embodiment of the present invention, the contents of Table 5 andTables 7-10 are known and/or kept by both the BS and the MS. With thisbasis, ‘Feedback type’ can be assigned using the subheader of Table 7while ‘Feedback content’ having a 6-bit length of Table 5 and Tables8-10 can be transmitted as feedback information according to theassigned ‘Feedback type.’ Based on such arrangement, various feedbacktypes can be transmitted via a single subheader. Table 5 and Tables 8-10are merely examples of feedback contents used to illustrate theembodiment of the present invention.

Preferably, the MIMO mode feedback subheader can include use a methodfor transmitting precoding weight/antenna weight used in the closed-loopMIMO system as well as the MIMO mode and permutation scheme. Inaddition, it is preferable to include an indicator for indicating indetail (e.g., more precisely) the method to be used for transmittingweight values from a plurality methods for transmitting precodingweight/antenna weight.

Furthermore, with respect to the directed precoding matrix value, it ispreferable to quantize the directly determined weight value and transmitthe quantized value using 6 bits per each element of the matrix.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of transmitting feedback information in a Multi-Input,Multi-Output (MIMO) system, the method comprising: receiving, by amobile station (MS), a feedback type field; and transmitting, by the MS,a Protocol Data Unit (PDU) that includes a Medium Access Channel (MAC)header, an extended subheader group and a payload, wherein the MACheader includes an Extended Subheader field (ESF) indicating that theextended subheader group is present in the PDU, wherein the extendedsubheader group appears immediately after the MAC header and comprises aMIMO mode feedback extended subheader, and wherein the MIMO modefeedback extended subheader comprises a feedback contents field thatincludes at least antenna grouping information, antenna selectioninformation, or reduced precoding matrix codebook information based onthe received feedback type field.
 2. The method according to claim 1,wherein the MIMO mode feedback extended subheader appears in a firstProtocol Data Unit (PDU) transmitted by the MS.
 3. A mobile station fortransmitting feedback information in a Multi-Input, Multi-Output (MIMO)system, the mobile station comprising: a transmission module fortransmitting a radio signal; and a reception module for receiving aradio signal, wherein the mobile station is configured to: receive afeedback type field via the reception module; and transmit a ProtocolData Unit (PDU) via the transmission module, the PDU including a MediumAccess Channel (MAC) header, an extended subheader group and a payload,wherein the MAC header includes an Extended Subheader field (ESF)indicating that the extended subheader group is present in the PDU,wherein the extended subheader group appears immediately after the MACheader and comprises a MIMO mode feedback extended subheader, andwherein the MIMO mode feedback extended subheader comprises a feedbackcontents field that includes at least antenna grouping information,antenna selection information, or reduced precoding matrix codebookinformation based on the received feedback type field.
 4. The mobilestation of claim 3, wherein the MIMO mode feedback extended subheaderappears in a first Protocol Data Unit (PDU) transmitted by the MS.
 5. Amethod of receiving feedback information in a Multi-Input, Multi-Output(MIMO) system, the method comprising: transmitting, by a base station(BS), a feedback type field; and receiving, by the BS, a Protocol DataUnit (PDU) that includes a Medium Access Channel (MAC) header, anextended subheader group and a payload, wherein the MAC header includesan Extended Subheader field (ESF) indicating that the extended subheadergroup is present in the PDU, wherein the extended subheader groupappears immediately after the MAC header and comprises a MIMO modefeedback extended subheader, and wherein the MIMO mode feedback extendedsubheader comprises a feedback contents field that includes at leastantenna grouping information, antenna selection information, or reducedprecoding matrix codebook information based on the feedback type field.6. The method according to claim 5, wherein the MIMO mode feedbackextended subheader appears in a first Protocol Data Unit (PDU)transmitted by the MS.
 7. A base station (BS) for transmitting feedbackinformation in a Multi-Input, Multi-Output (MIMO) system, the BScomprising: a transmission module for transmitting a radio signal; and areception module for receiving a radio signal, wherein the BS isconfigured to: transmit a feedback type field via the transmissionmodule; and receive a Protocol Data Unit (PDU) via the reception module,the PDU including a Medium Access Channel (MAC) header, an extendedsubheader group and a payload, wherein the MAC header includes anExtended Subheader field (ESF) indicating that the extended subheadergroup is present in the PDU, wherein the extended subheader groupappears immediately after the MAC header and comprises a MIMO modefeedback extended subheader, and wherein the MIMO mode feedback extendedsubheader comprises a feedback contents field that includes at leastantenna grouping information, antenna selection information, or reducedprecoding matrix codebook information based on the feedback type field.8. The base station of claim 7, wherein the MIMO mode feedback extendedsubheader appears in a first Protocol Data Unit (PDU) transmitted by theMS.